Vibrating apparatus control



July 18, 1933. e. F. DODGE VIBRATING APPARATUS CONTROL i ulllllmlm ANODE VOLTAGE All"!!! GRID Vol. 7465 ANODE VOLTAGE Filed July 22, 1952 FREQUENCY GR/D VOL TAGE INVENTOR, @QQDQW F. 00065.

@wizw ATTORNEY Patented July 18, 1933 UNITED STATES GORDON I. DODGE, OF OAKLAND, CALIFORNIA VIBRATING APPARATUS CONTROL Application filed July 22, 1982. Serial No. 823,870.

My invention relates to a vibrating apparatus control and more particularly to a control for regulating and maintaining a constant stroke of the moving member of separating t screens, feeders, conveyers, and like machines.

Among the objects of my invention are: To provide a simple and controllable source of pulsating direct current to operate a vibrating apparatus to provide a means of controlling the stroke of a vibrating a(pparatus in accordance with a varying loa to provide apparatus for maintaining the stroke of a vibrating mechanism constant regardless of load; to provide a means of regulating the stroke of a vibrating member driven by an electromagnet; to provide a vibrating member driven by a pulsating current, which will not resonate with the driving frequency when variously loaded; and to provide an electrostatically controlled arc rectifier as a source of power for the operation of a vibrating apparatus, the rectifier being under control of the apparatus to maintain a uniform stroke.

25 Other objects ofmy invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of my invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawing:

Figure 1 is aiside view in elevation, partly schematic, of atvibrating screen showing the I resilient suspension.

Figure 2 is a top view of the screen shown in Figure 1.

Figure 3 is a schematic circuit diagram, reduced to its lowest terms, of an electrostatically controlled arc rectifier as used in conjunction with the shalriar shown in Figure 1.

Figure 4 is a diagram representing several resonance curves obtained from a resiliently mounted screen with difi'erent loads.

Figure 5 is a diagram representing the contol characteristics of the rectifier when the grid voltage is in phase with the anode volt- ,5 "Figure 6 is a diagram representing the control characteristics of the rectifier when the grid voltage is retarded in phase.

In previous machines having a moving element electromagnetically operated for use as screen, feeders, conveyers, or the like, it has been the practice to energize the driving magnets from a frequency chan er to reduce the number of impulses norma ly produced by the usual 50 to cycle current. It is also common to use a motor generator to superimpose a direct current on the alternating current 1n the driving ma et, so that in both cases only 50 or 60 stro es a second will be produced.- In such instances manual control of the initial power input may be had, but no satisfactory method has been used to vary the power supplied to the driving magnet to make up for the loss of strike due to heavy loads being suddenly applied to the vibrating member.

In screening or conveying gravel, loads are usually intermittent and vary widely from nothing up to the maximum capacity of the machine. Under these circumstances, in case of a feeder or conveyer mechanism, for example, exceedingly rapid transport will occur when lightly loaded, but almost no forward progress will take place under heavy loads.

Broadly speaking, my invention comprises a vibrating apparatus driven by an electromagnet receiving the pulsating d. 0. output of an electrostatically controlled arc rectifier operated from the commercial a. c. mains of 25, 50 or 6() cycle frequency. The vibrating member is connected to cause a change in the control circuit of the rectifier whereby more or less current is supplied by the rectifier to the driving magnet in accordance with the load on the vibrating member. The stroke is thus automatically maintained constant, and means are provided for initially adjusting the length of stroke, or changing the degrceof stroke it is desired to maintain, even during operation of the apparatus, In addition I carefully adjust the resonance points of the vibrating members plus all available loads so that they cannot coincide with the driving frequency at any time, and

thus prevent resonance peaks, and consequent disturbance of operation.

Referring to the drawing, which illustrates one application of my invention a vibrating screen for separating or conveying gravels, a foundation frame 1, preferably solidly built up from angle-iron or structural steel, has several spring brackets 2 secured to the top surface of the sides of the frame by rivets 4. These brackets support pans of resilient members 5, usually made from spring steel assembled in leaf form, and are held in place by spring rivets 6. A screen frame 7 also made from angle-iron, is fastened to the upper end of the springs by means of screen brackets 9, riveted both to the springs and the screen frame. The angle of the springs will determine the forward throw of the particles to be shaken and varies somewhat according to the degree of progression or shaking desired.

The screen frame is covered with a separating or progression screen 10 of wire mesh whose dimensions will vary with different uses and materials.

It will be noted that while only three pairs of resilient members are shown fastened to a short screen, such screens may in practice he of considerable length and have a multilicit of s rin sup rts.

p At due and of %he fO ZSIdIItiOD frame is fixed a drivingmagnet bracket 11 to which is fixed an electrbmagnet core 12 of soft iron, preferably laminated and of horseshoe shape, each leg being inserted in field windings 14, connected in series. Firmly attached to the screen frame is a laminated soft iron armature 15 located close to and bridging the airgap between the core legs. A sufficient airgap is left between the armature and the core to allow for maximum stroke of the screen frame.

Also attached to the moving frame at or near the armature is a control arm 16, shown diagrammatically as attached to the armature in Figures 2 and 3. This arm contacts the top of a variable resistor 17 preferably of the carbon pile type. The pressure of this resistor and consequent resistance will depend on the length of stroke of the armature or frame. It is desirable that some spring action be built into the arm in order to partially filter the stroke action to avoid heavy stresses on the resistor, and to average the response.

The arm 17 is not directly attached to the pile, and so does not tend to open the resister on the back stroke. I also prefer to attach to the top of pile a pair of dash-pots 18 which will allow the pile to be compressed by the arm 17, but which will retard the opening of the pile on the backstroke. Thus, the resistance of the pile will be maintained substantially uniform and constant at a given stroke and proportional to the length of stroke as it changes. The slight lag introduced by the dash-pots is not objectionable, as only a few cycles of changed stroke are necessary for the pile a, establish its new resistance.

The combination of spring arm and dashpot efi'ectively constitute a mechanical filter and rectifier, and such small variations in resistance as do remain due to the individual strokes, are of such low magnitude as to be unimportant in the control of the apparatus.

Power for operation of the electroma et is supplied by a hot cathode electrostatical- 1y controlled arc rectifier 19. This rectifier comprises an envelope 20 containing mercury vapor or other inert gas, and three electrodes; a hot cathode 21, an anode 22 and a grid or control electrode 24. Such tubes are available up to 200 k. w. output.

The current passes through the tube as an arc whose starting may be controlled by the grid. After starting it can be stopped by removing the anode voltage. A perfect control of rectifier output may be obtained b impressing alternating voltage on hot anode and grid and varying the phase of the grid voltage with respect to that of the anode whereby the output current can be varied from zero to full value.

Figures 5 and 6 show two typical stages in this type of control. Figure 5 shows the grid voltage in phase with the anode voltage, and current starts at the beginning and flows during the whole of the half cycle, while Figure 6 shows the grid voltage advanced in phase so that the current does not start until late in the cycle, as current cannot flow until the grid becomes positive. The power output of the tube is thus varied.

A preferred method of changing the phase is shown in Figure 3. This is a diagram of a series combination of inductance and resistance.

Alternating current from ,25, or cycle mains is supplied to the primary 25 of a transformer 26. One end of the secondary 27 passes through a manually variable resistor 29 and the carbon pile resistor 17 and thence to the grid. The opposite end of the transformer passes through the windings of the electromagnet to the anode, and an inductance 30 is bridged across between the anode end of the transformer and the grid. The cathode is connected to the center of the transformer, and supplied with current from the mains 33.

In this circuit, as the resistance of the manually variable resistor plus that of the carbon pile is varied from zero to infinity, the alternating voltage between cathode and grid remains constant in amplitude but is progressively advanced through 180 in phase.

As the output of the tube is proportional to this change in phase, it follows that the rectified power supplied to the electromagnet will depend on the resistances of the manually 'at any time, before or urmg operation; and

that the carbon pile resistance, varied by that stroke by changing phase on the grid Wlll automatically maintain the normal stroke indefinitely, as a reduction of stroke due to the sudden acquisition of a heavy load by the screen will cause the carbon pile pressure and consequent resistance to change, which in turn will shift the phase to cause greater rectifier output to act on the magnet. The converse will be equally efiective to avoid an increase in stroke.

If at any time I find that material delivered to the shaking device necessitates a shorter or longer stroke in order to be properly handled, I may change the manual resistor to cause that change of stroke. As the change of stroke may be made without shutdown of the shaker, it is obvious that much time can be saved, and widely varying materials can be run through in a minimum of time.

Other combinations of resistance, inductauce and capacity, one of which is varied by the stroke to change the phase of the rectifier may be used, without departing from the spirit of my invention.

Another factor that must be taken into account in producing a uniform stroke regard less of load, is the resonance of the vibrating members.

Figure 4 is a schematic diagram representing the resonant peaks of the vibrating memher under various loads. I have found that by properly adjusting spring tensions I am able to confine the entire family of resonance peaks which are caused by the weight of the springs and moving frame added to the eficct of the superimposed loads, to a band of frequencies apart from that used to energize the driving magnet.

In Figure 4 the response to 60 cycles is not very different with load variations from zero to maximum as indicated by curves A, B and C. A uniform stroke will thus be obtained irrespective of load. Other support tensions and adjustments will be used when a driving frequency of 25 or 50 cycles is contemplated, and the same procedure followed.

\Vhile I realize that such a setting, apart as it is from any resonance peak, is wasteful of driving power, I consider the many and obvious advantages of obtaining a uniform response to varying loads to far outweigh such power losses, particularly when used in con'unction with my control circuit as descri I claim:

1. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power movement of said element, a rectifier having a power output circuit and a control circuit,- means for supplying rectified alternating current from said rectifier to said magnet, and means connected to said control circuit to vary the output of said rectifier in accordance with said load.

2. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to client power movement, of said element, a rectifier having a power output circuit and a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, and means operated by said vibrating element connected to said control circuit to vary the output of said rectifier in accordance with said load.

3. In combination with a vibrating apparatus, an element to be vibrated under a varying load, a rectifier having a power output circuit and a control circuit, means for supplying alternating current to said output circuit and said control circuit, means for vibrating said element comprising an electromagnet energized by the output of said rectifier, and means connected to said element to change the phase relation of said output and control circuits in accordance with said load, to maintain a constant stroke of said element.

4. In combination with a vibrating apparatus, an element to be vibrated under a varying load, a rectifier having a power output circuit and a control circuit, means for supplying alternating current to said output circuit and said control circuit, means for vibrating said element comprising an electromagnet energized by the output of said rectifier, means connected to said element to change the phase relation of said output and control circuits in accordance with said load, to maint"in a constant stroke of said element, and means for predetermining the extent of said stroke.

5. In combination with a vibrating apparatus, an element to'be vibrated under a varying load, a rectifier having a power output circuit and a control circuit, means for supplying alternating current to said output circuit and said control circuit, means for vibrating said clement comprising an electromagnet energized by the output of said rectifier, means connected to said element to change the phase relation of said output and control circuits in accordance with said load, to maintain a constant stroke of said element, and means for changing said stroke during theoperation of said apparatus.

6. Vibrating apparatus comprising a memher, adapted to be loaded, electromagnetic means for imparting reciprocatory movements to said member, a rectifier for supplying said electromagnetic means with a pulsating direct current, and means to control the output of said rectifier in accordance with the load on said member.

7 Vibrating apparatus comprising a member adapted to be loaded, electromagnetic means for imparting reciprocatory movements to said member, a rectifier for supplying said electromagnetic means with a pulsating direct current, means to control the output of said rectifier in accordance with the load on said member, and means for regulating the extent of said reciprocatory movement.

8. The method of maintaining a constant stroke under varying loads in a vibrating apparatus driven by electromagnetic means connected to an alternating current rectifier which comprises controlling the output of said rectifier in accordance with the stroke of said vibrating apparatus.

9. The method of maintaining a constant stroke under a varying load in a vibrating apparatus driven by the output of a grid controlled alternating current rectifier which comprises controlling the grid of said rectifier in accordance with the stroke of said v1- brating apparatus, and operating said rectifier at a. frequency different from any resonant period formed by the combination of said vibrating apparatus and its loads.

10. In combination, vibrating apparatus comprising a member adapted to be variably loaded, an electromagnet for imparting reciprocatory movements to said member, an electrostatically controlled arc rectifier for supplying a pulsating direct current to said electromagnet from an alternating current source, and means actuated by said reciprocatory movements to control the output of said rectifier to maintain a uniform stroke of said member during the variation of load.

11. In combination, vibrating apparatus comprising a member adapted to be variably loaded, an electromagnet for imparting reciprocatory movements to said member, an electrostatically controlled are rectifier for supplying a pulsating direct current to said electromagnet from an alternating current source, means actuated by said reciprocatory movements to control the output of said rectifier to maintain a uniform stroke of said member during the variation of load, and means for adjusting the extent of said stroke.

12. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative efl'ect power movement of said element, a rectifier having a power output circuit and a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, a pressure variable resistor connected to change the phase of said control circuit, and means for resilientl connecting said vibrating element to said resistor to cause a change in resistance when the length of said power movement is changed.

13. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power 1110 vement of said element, :1 rectifier having a power output circuit and a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, a pressure operated variable resistor connected to change the phase of said rectifier, and means for applying pressure to said reslstor in proportion to the extent of vibration of said element.

x 14. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power movement of said element, a rectifier having a power output circuit and a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, a resilient arm attached to said vibrating element, a resistance changeable by the pressure of said arm in accordance with the stroke of said vibrating element, and means for connecting said resistance in said control circuit to vary the output of said rectifier. I

15. The method of maintaining a constant stroke under a varying load in a vibrating apparatus driven by-the output of a grid controlled alternating current rectifier which comprises controlling the grid of said rectifier in accordance with the stroke of said vibrating apparatus.

16. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power movement of said element, a rectifier having a power output circuit and a control circuit, means for supplyin rectified alternating current from said rectih er to said magnet, a resilient arm attached to said vibrating element, a resistance changeable by the pressure of said arm in accordance with the stroke of said vibrating element, means for connecting said resistance in said control circuit to vary the output of said rectifier, and means for averaging the response of said resistance.

17. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power movement of said element, a rectifier having a power output circuit and a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, a resilient arm attached to said vibrating element, a resistance changeable by the pressure of said arm in accordance with the stroke of said vibrating element, means for connecting said resistance in said control circuit to vary the output of said rectifier, and

a mechanical filter secured to said pile to minimize the change of resistance due to the individual strokes of said element.

18. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power movement of said element, a rectifier having a po yyer output circuitand a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, a pressure operated variable resistor connected to change the phase of said rectifier, means for applying pressure to said resistor in proportion to the extent of vibration of said elment, and means for averaging said pressure.

19. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to efiect power movement of said element, a rectifier having a power output circuit and a control circuit, means for supplying rectified alternating current from said rectifier to said magnet, a pressure operated variable resistor connected to change the phase of said rectifier, and means for applying pressure on the power stroke to said resistor in proportion to the extent of vibration of said element.

20. In a vibrating apparatus, the combination of an element to be vibrated under a varying load, an electromagnet operative to effect power movement of said element, a rectifier having a power output circuit and a control circuit, means for supplyin rectified alternating current from said recti er to said magnet, a pressure operated variable resistor connected to change the phase of said rectifier, means for applying pressure on the power stroke to said resistor in proportion to the extent of vibration of said element, and means for averaging said pressure.

GORDON F. DODGE, 

